Move etcd docsy-deltas into themes/docsy

[chalin]

• Closes Complete file setup for proper use of cncf/docsy #431
• Contributes to Upgrade docsy #494
• No change in generated site files except for the CSS map:

> (cd public && git diff | head -14)

diff --git a/scss/main.css.map b/scss/main.css.map
index 2b398c61..c468fb84 100644
--- a/scss/main.css.map
+++ b/scss/main.css.map
@@ -123,7 +123,7 @@
                "themes/docsy/assets/scss/_sidebar-toc.scss",
                "themes/docsy/assets/scss/_buttons.scss",
                "themes/docsy/assets/scss/_breadcrumb.scss",
-               "assets/scss/_alerts.scss",
+               "themes/docsy/assets/scss/_alerts.scss",
                "themes/docsy/assets/scss/_content.scss",
                "themes/docsy/assets/scss/_search.scss",
                "themes/docsy/assets/scss/_main-container.scss",
@@ -256,7 +256,7 @@

[chalin]

Need to build atop of this. Given that there are no changes to the generated site files, I'll merge now. Comments are still welcome.